Optical temperature measurement techniques utilizing phosphors

ABSTRACT

A technique of temperature measurement wherein an object or environment to be measured is provided with a phosphor material layer that emits at least two optically isolatable wavelength ranges whose intensity ratio depends upon the object or environment temperature, the emitted radiation being brought to a detector by an optical system that may include an optical fiber. Several specific applications of this technique are disclosed, such as temperature monitoring of electrical equipment and industrial processing, medical temperature instrumentation including the use of disposable elements that contain a small quantity of the temperature dependent phosphor, special and multiple probes, the use of liquid phosphors, and a phosphor paint for monitoring surface temperatures.

This is a division of Application Ser. No. 167,691, filed July 10, 1980,now U.S. Pat. No. 4,448,547, which is a continuation-in-part ofapplication Ser. No. 877,977, filed Feb. 15, 1978, now U.S. Pat. No.4,215,275, which in turn is a continuation-in-part of application Ser.No. 751,366, filed Dec. 16, 1976, now U.S. Pat. No. 4,075,493.

BACKGROUND OF THE INVENTION

This invention relates generally to devices and methods for makingtemperature measurements, and more specifically to devices and methodsthat make such measurements by optical techniques that utilizetemperature-sensitive phosphors.

There are many methods currently used for temperature measurement. Themost common techniques utilize thermocouples, thermistors or resistancethermometers by means of which electrical signals are generated and thenconverted into temperature readings or employed for control functions.

On occasion, however, it is useful, and sometimes essential, to obtaintemperature data by non-electrical techniques. This may occur: (1) wheretemperatures over large areas are to be measured and measurement by adense distribution of thermocouples thus becomes impractical; (2) wherethe attachment of thermocouples and leads would alter the temperaturesto be measured; (3) in environments where, because of high electric ormagnetic fields, metallic wires are undesirable; (4) where electricalisolation and/or insensitivity to electrical noise generation isdesired; (5) where, because of motion or remoteness of the part to besensed, permanent lead wires are impractical; or (6) where, because ofcorrosive chemical environments, wires and thermocouple junctions wouldbe adversely affected, with resultant changes in electricalcharacteristics. In these situations, optical techniques frequentlybecome preferable.

The most direct optical technique for temperature measurement isinfrared radiometry. However, where line of sight measurement is notpossible, without infrared transmission media, the infrared techniquessuffer a disadvantage. In such an instance there are relatively fewmaterials sufficiently transparent to long-wave infrared radiation toprovide an infrared conducting path from the area where temperature isto be sensed to the infrared detector. Furthermore, infrared techniquesare not absolute in that the emissivity of the emitting material has tobe known accurately if the infrared radiometric measurements are to beconverted into true temperature readings.

Optical pyrometers can also be used, but only for very hot sources whichemit visible radiation. Optical pyrometers also suffer from the sameproblems as infrared radiometers when it comes to absolute measurements.

For large area measurements, thermographic phosphors or liquid crystalsare sometimes employed in the form of films, paint or coatings appliedto the surface to be measured. Known typical thermographic phosphorsexhibit a broad fluorescence under ultraviolet excitation, thisfluorescence being strongly temperature-dependent with regard toemission intensity. The fluorescent intensity of this emission"quenches" sharply as the temperature rises over a fairly narrowtemperature range. It is difficult to calibrate a thermographic phosphorabsolutely because changes in excitation, such as might be caused bysource instability, can be misinterpreted as a temperature variation.Liquid crystals change their reflected colors with temperature over asimilarly narrow range. Both materials suffer from the fact that, toachieve high sensitivity, the range over which the material will operateas temperature sensors is of necessity fairly restricted compared withthe materials of this invention. Most liquid crystal materials are alsorelatively unstable and may change their chemical and physicalproperties over a period of time. While this is not always a problem, itcan be in selected applications.

Therefore, it is a primary object of the present invention to providemethods and systems for remote temperature measurement using optical,rather than electrical, techniques that permit elimination of metallicwires, junctions and connectors, that circumvent electrical noisesources and that provide for measurement over extended areas as well aspoint measurements.

It is another object of the present invention to provide an internallycalibrated phosphor temperature measuring system whereby changes intotal fluorescent intensity with time as might be caused by a variationin excitation, changes in optical transmission with time or changes insensitivity of a receiving detector with time are not interpreted astemperature changes.

It is yet another object of the present invention to provide a means ofmeasuring temperatures of objects or environments without the necessityof direct physical contact with electrical wires, such as situationswhere the point to be measured is submerged in a corrosive gas orliquid, must be isolated electrically or thermally, is in a vacuum, oris located on a moving part to which permanent leads cannot beconveniently connected.

It is a further object of the present invention to provide techniquesadapted for medical and clinical temperature measurement applications.

It is also an object of the present invention to provide a means ofmaking absolute, internally calibrated temperature measurements overwider temperature ranges than would be possible with conventionalthermographic phosphors or liquid crystals.

Finally, it is an object of the present invention to provide uniquearrangements and temperature measuring applications of conventionalthermographic phosphors.

SUMMARY OF THE INVENTION

These and additional objects are accomplished by the techniques of thepresent invention wherein, generally, according to one aspect thereof,an object or environment for which a temperature is to be measured isplaced in thermal contact with phosphor material that when excited toluminescence emits detectable radiation within two or more distinctwavelength ranges that are optically isolatable from one another, with arelative intensity of emission in these wavelength ranges varying in aknown manner as a function of the temperature of the phosphor. Sharpline emitting phosphors, such as those having rare earth activators, arepreferred. A practical system of accurately measuring temperatures overwide ranges is thus made possible, a normal desired range of from -100°C. to +400° C. being achievable.

The intensity of two such lines of phosphor emission are detected and aratio of the detected signals taken. The ratio is convertible intotemperature in accordance with the known temperature characteristics ofthe phosphor material. This optical system is internally calibratedbecause the taking of a ratio makes the technique relatively insensitiveto changes in total intensity of the phosphor emissions, general changesin optical transmission, or changes in the sensitivity of the receivingdetector which may occur in time. The technique is thus adapted for longterm remote temperature measurement applications. It also makes feasiblethe manufacture of interchangeable or disposable sensors such as probes,paints, adhesive spots, etc., wherein the light output may vary fromprobe to probe whereas the ratio may be unaffected.

The phosphor temperature sensor is excitable to luminescence byelectromagnetic radiation in the visible or near-visible portion of thespectrum in order that standard optical elements may be employed. Thepreferred phosphor is also characterized by emitting useful temperaturedependent lines at much different wavelengths than that of the excitingradiation. This characteristic allows easy elimination of the excitingradiation from the luminescent radiation detectors. However, other moreconventional phosphors can also be utilized.

The use of this approach permits several specific temperaturemeasurement improvements and solves heretofore unsolved temperaturemeasuring problems. According to one specific form of the invention,remote, non-contact temperature measurements can be made of largesurface areas, such as those in models being tested in wind tunnels, byapplying a phosphor paint over the surface areas to be monitored. Themodel or other surface is then illuminated by an appropriate excitingradiation and intensity measurements of the selected phosphorluminescent lines are taken of selected points on the surface from adistance removed from it.

According to another specific aspect of the invention, remotemeasurement of point temperatures are made possible. According to thepresent invention, the phosphor material is formed internal to a smallsensor on the end of a fiber optic cable. The sensor is then immersed inthe location where a point temperature measurement is needed. Thephosphor is coupled to the detector by means of the fiber optic cablewith the measurements of the phosphor luminescence being made at adistance from the measurement location.

The techniques of the present invention also have advantages inapplications where distance of the measuring location from the detectionstation is not of principal concern. In medical applications, forexample, the improved measurement precision and short response timeprovided by the present invention is among several substantialadvantages. Routine human temperature measurements may be made with anoptical fiber end covered by a disposable probe cover that contains asmall quantity of phosphor. Hyperthermia treatment of a human may beprecisely monitored by fiber optic lengths having their phosphor-coatedends implanted at different locations within the patient. Medical andnon-medical temperature measurements of moving objects, sample cells orcontainers can also advantageously utilize the techniques of the presentinvention that utilize both conventional thermographic phosphors and thepreferred sharp emission line phosphors described in detail herein.

Disposable substrates with a quantity of phosphor carried thereby arealso a part of the present invention. The ratioing system of the presentinvention, in which such substrates are employed, automaticallycalibrates for any differences in emission level of the phosphor, thusproviding a high tolerance to variations in manufacturing of thedisposable substrates. The substrates can be in the form of atemperature probe, probe cover, length of optical fiber, liquid contactbeads, bag or other container, or even a thin sheet with adhesive forplacement on any surface desired to be monitored. A simpler detectiontechnique, in which a single emission wavelength range is sensed such aswith a more conventional phosphor compound, may also advantageously beemployed in these unique applications without ratioing intensities ofdifferent emission bandwidths, but the calibration of such a system ismore difficult.

The temperature sensing techniques described herein have significantadvantages for operating in environments of high electric or magneticfields or in the presence of strong electromagnetic radiation. Thephosphor selected for such an environment has detected optical emissionsthat are unaffected by the environment.

Many of the features described herein and other features and details ofthe invention are set forth in an article entitled "Recent Advances inOptical Temperature Measurements" by applicant and another, appearing inthe December, 1979 issue of Industrial Research/Development, pages82-89, which article is incorporated herein by reference.

The present invention has been described only very generally. Additionalobjects, advantages and features thereof are set forth as part of thefollowing description of the preferred embodiments of the variousaspects of the present invention, which should be taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating in general the basic aspects ofthe present invention;

FIG. 2 are curves that illustrate the fluorescent emission spectrum attwo different temperatures of a europium-doped lanthanum oxysulfidephosphor when excited by ultraviolet radiation;

FIG. 3 are curves that illustrate the intensity of specific strongemission lines from certain rare earth oxysulfide phosphors when excitedby suitable radiation;

FIG. 3A is a sample excitation spectrum for a rare earth oxysulfidemeasured at a single radiation output line;

FIG. 4 schematically illustrates one specific form of the presentinvention wherein the temperature of the surface of a wind tunnel modelis remotely measured;

FIG. 5 shows one specific form of an optical detector 103 of thetemperature measuring system of FIG. 4;

FIG. 6 shows another specific form of an optical detector 103 of thetemperature measurement system of FIG. 4;

FIG. 7 schematically illustrates a large electrical power transformerutilizing one aspect of the present invention for remotely measuringspot temperatures thereof;

FIG. 8 shows a phosphor temperature sensor and optical system thereforas one form of the temperature measurement system of FIG. 7;

FIG. 8A illustrates a modification of the temperature measurement systemof FIG. 8;

FIG. 9 shows a variation in the temperature measurement system of FIG.8;

FIG. 10 shows yet another variation of the temperature measurementsystem of FIG. 8 utilizing multiple sensors;

FIGS. 10A, 10B and 10C show multiplexing systems for multiple sensors;

FIG. 11 illustrates a rotating device with its internal temperaturebeing measured according to another aspect of the present invention;

FIG. 12 illustrates a moving belt with its temperature being measuredaccording to another aspect of the present invention;

FIGS. 13 and 13A illustrate another aspect of the present inventionwherein the temperature of fluid is measured;

FIGS. 14 and 14A illustrate the present invention applied to a systemincluding a removeable temperature probe sleeve;

FIGS. 15 and 15A illustrate the present invention in an applicationmonitoring an internal temperature of a living organism or otherbiological specimen that is under heat treatment;

FIG. 16 shows an enlarged optical fiber end forming a temperaturesensor;

FIGS. 16A and 16B illustrate a multi-sensor fiber optic probe;

FIGS. 17, 18 and 19 illustrate adhesive phosphor carriers and their use;

FIGS. 20 and 20A illustrate disposable containers having phosphortemperature sensors;

FIG. 21 shows a high temperature probe; and

FIGS. 22 and 22A show a probe for detecting the temperature of a movingobject or material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the system aspect of the present invention isillustrated. Within some environment 1 is positioned a solid object 20having a phosphor coating 40 over at least a portion thereof. Thephosphor is characterized by emitting, when excited, electro-magneticradiation within separable bandwidths at two or more distinctwavelengths and with relative intensities in those bands that vary as aknown function of the temperature of the phosphor 40. Thus, thetemperature of the phosphor 40 is detected that is the same as orrelated to that of the object 20, and in some applications of theenvironment 1 as well.

Such luminescent emission of the phosphor 40 in the form ofelectromagnetic radiation 41, generally in or near the visible spectrum,is excited by a source 60 over a path 61. The source could beradioactive material, a source of cathode rays, an ultravioletelectromagnetic energy source, or any other remote source producingefficient fluorescence depending upon the particular type of phosphorutilized in the preferred forms of the present invention. The relativeintensities of two distinct wavelength bands within the emittedradiation 41 contains the desired temperature information.

The emitted radiation 41 is gathered by an optical system 80 anddirected in a form 81 onto an optical filter and radiation detectorblock 100. The block 100 contains filters to isolate each of the twobands or lines of interest within the radiation 81 that contain thetemperature information. After isolation, the intensity of each of thesebands or lines is detected which results in two separate electricalsignals in lines 101 and 102, one signal proportional to the intensityof the radiation in one of the two bands and the other signalproportional to the intensity of the radiation in the other of the twobands of interest.

These electrical signals are then applied to an electronic signalprocessing circuit 120. In a preferred form, the signal processingcircuits 120 take a ratio of the signals in the lines 101 and 102 by theuse of routinely available circuitry. This electronic ratio signal isthen applied to a signal processor within the block 120. The signalprocessor is an analog or digital device which contains atherelationship of the ratio of the two line intensities as a function oftemperature for the particular phosphor 40 utilized. This function isobtained by calibration data for the particular phosphor 40. The outputof the signal processor in a line 121 is thence representative of thetemperature of the phosphor 40.

The signal in the line 121 is applied to a read out device 140 whichdisplays the temperature of the phosphor 40. The device 140 could be anyone of a number of known read out devices, such as a digital or analogdisplay of the temperature over some defined range. The device 140 couldeven be as elaborate as a color encoded television picture wherein eachcolor represents a narrow temperature range on the object. It could alsobe a television picture stored on disc or tape. It might also be a chartrecorder or the input to a control system.

PREFERRED PHOSPHOR MATERIALS AND CHARACTERISTICS

The fundamental characteristics of a preferred phosphor material for usein the present invention is that when properly excited it emitsradiation in at least two different wavelength ranges that are opticallyisolatable from one another, and further that the intensity variationsof the radiation within each of these at least two wavelength ranges asa function of the phosphor temperature are known and different from oneanother. A phosphor material is preferred that is further characterizedby its radiation emission in each of these at least two wavelength bandsbeing sharp lines that rise from substantially zero emission on eitherside to a maximum line intensity, all in less than 100 angstroms. Thelines are easy to isolate and have their own defined bandwidth. Butmixtures of broadband emitters, such as of more conventional non-rareearth phosphors, are also usable so long as two different wavelengthranges of emission of the two materials can be separated sufficientlyfrom one another so that an intensity ratio can be taken, and as long asthe temperature dependences for thermal quenching are sufficientlydifferent for the two phosphors.

For a practical temperature measuring device, the phosphor materialselected should also emit radiation in the visible or near visibleregion of the spectrum since this is the easiest radiation to detectwith available detectors, and since radiation in this region is readilytransmitted by glass or quartz windows, fibers, lenses, etc. It is alsodesirable that the phosphor material selected be an efficient emitter ofsuch radiation in response to some useful and practical form ofexcitation of the phosphor material. The particular phosphor material ormixture of phosphor materials is also desirably chosen so that therelative change of intensity of emission of radiation within the twowavelength ranges is a maximum within the temperature range to bemeasured. The phosphor material should also be durable, stable and becapable of reproducing essentially the same results from batch to batch.In the case of fiber optic transmission of the phosphor emission, asdescribed in specific embodiments hereinafter, a sharp line emittingphosphor is desirably selected with the lines having wavelengths nearone another so that any wavelength dependent attenuation of the fiberoptic will not significantly affect the measured results at a positionremote from the phosphor, thereby eliminating or reducing the necessityfor intensity compensation that might be necessary if fibers of varyinglengths were used.

The composition of a phosphor material capable of providing thecharacteristics outlined above may be represented very generally by thegeneric chemical compound description A_(x) B_(y) C_(z), wherein Arepresents one or more cations, B represents one or more anions, A and Btogether forming an appropriate non-metallic host compound, and Crepresents one or more activator elements that are compatable with thehost material. x and y are small integers and z is typically in therange of a few hundredths or less.

There are a large number of known existing phosphor compounds from whichthose satisfying the fundamental characteristic discussed above may beselected by a trial and error process. A preferred group of elementsfrom which the activator element C is chosen is any of the rare earthions having an unfilled f-electron shell, all of which have sharpisolatable fluorescent emission lines of 10 angstroms bandwidth or less.Certain of these rare earth ions having comparatively strong visible ornear visible emission are preferred for convenience of detecting, andthey are typically in the trivalent form: praseodymium (Pr), samarium(Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er) and thulium (Tm). Other activators such as neodymium (Nd) andytterbium (Yb) might also be useful if infra-red sensitive detectors areused. Other non-rare earth activators having a characteristic of sharpline emission which might be potentially useful in the present inventionwould include uranium (U) and chromium (Cr³⁺). The activator ion iscombined with a compatable host material with a concentration ofsomething less than 10 atom percent relative to the other cationspresent, and more usually less than 1 atom percent, depending on theparticular activator elements and host compounds chosen.

A specific class of compositions which might be included in the phosphorlayer 40 is a rare earth phosphor having the composition (RE)₂ O₂ S:X,wherein RE is one element selected from the group consisting oflanthanum (La), gadolinium (Gd) and yttrium (Y), and X is one dopingelement selected from the group of rare earth elements listed in thepreceeding paragraph having a concentration in the range of 0.01 to 10.0atom percent as a substitute for the RE element. A more usual portion ofthat concentration range will be a few atom percent and in some casesless than 0.1 atom percent. The concentration is selected for theparticular emission characteristics desired for a given application.

Such a phosphor compound may be suspended in an organic binder, asilicone resin binder or a potassium silicate binder. Certain of thesebinders may be the vehicle for a paint which can be maintained in aliquid state until thinly spread over a surface whose temperature is tobe measured where it will dry and thus hold the phosphor on the surfacein heat conductive contact with it.

A specific example of such a material for the phosphor layer 40 of FIG.1 that is very good for many applications is europium-doped lanthanumoxysulfide (La₂ O₂ S:Eu) where europium is present in the range of a fewatom percent down to 0.01 atom percent as a substitute for lanthanum.The curves 42 and 43 of FIG. 2 provide, for two separate phosphortemperatures, the intensity of its emission as a function of wavelength.The phosphor was in the form of a finely crystalline powder and wasexcited by electrons. The emitted radiation was analyzed with a scanningmonochromator followed by a photomultiplier detector. The particularmaterial for which FIG. 2 illustrates the fluorescent emission spectrumis lanthanum oxysulfide with 0.1 atom percent of europium substitutedfor lanthanum.

Curve 42 of FIG. 2 shows the emission spectra of such a material at 295°K. which is room temperature. The curve 43 of FIG. 2 shows the emissionspectra for the material at 77° K., the extremely cold temperature ofliquid nitrogen. It will be noted that the spectral characteristics ofthe emission are much different at these two temperatures and thesechanges continue to occur as the phosphor is raised above roomtemperature.

Narrow wavelength fluorescent lines which are particularly useful fortemperature measurement, as marked on the curves of FIG. 2, are locatedat approximately 4680 angstroms, 5379 angstroms, 5861 angstroms(actually a doublet) and 6157 angstroms. The relative intensities ofthese lines change as a function of temperature of the phosphor and itis these relative intensities that give the temperature information inthe various forms of the present invention.

The relative intensities of at least two suitable narrow bandwidthspectral lines are determined, in the preferred forms of the invention,by taking the ratio of the detected intensities of two of the lines. Thetwo lines should thus preferably be non-overlapping and separated enoughin wavelength so that their intensities may be measured relativelyindependently. Referring to FIG. 3, the intensities of the four spectrallines identified on FIG. 2 are drawn as a function of temperature of thephosphor (curves 51, 53 and 54). Additionally, curve 44 of FIG. 3 showsa ratio of the intensities of the two spectral lines 52 and 51respectively at 5379 angstroms and 4680 angstroms as a function oftemperature. It is such a characteristic as illustrated by the curve 44that permits accurate temperature measurement by taking a ratio ofintensities of two spectral lines. Similarly, if the intensities of theother two lines 52 and 51 respectively at 6157 angstroms and 5861angstroms are ratioed, the characteristics of the resulting ratio as afunction of temperature is given in curve 45. As can be seen from FIG.3, the ratio represented by the curve 44 varies strongly within atemperature range of from -75° C. to +50° C. The second ratio indicatedby the curve 45, on the other hand, varies strongly with temperatureover the range of from about 50° C. to 300° C. Therefore, the particularfluorescent emission lines of the phosphor that are utilized depend uponthe expected temperature range to be monitored.

It has been found that the use of various pairs of the rare earthphosphor lines at 5140 (blue-green), 5379 (green) and 6280 (red)angstroms has certain advantages. One advantage is that these threelines are among the more intense lines common to all three oxysulfidehosts (lanthanum, gadolinium and yttrium). This allows a singleinstrument to be used will all three types of rare earth phosphors,although a different temperature calibration is necessary when thephosphor sensor material is changed. While the 4680 angstrom line is atleast comparable in intensity to the 5140 angstrom line, its use withvisible pumping involving excitation at approximately 4680 angstromswould make separation of exciting and fluorescent radiation moredifficult. Another advantage of this particular set of lines is thatthey are well separated in wavelength from lines of differenttemperature dependence and so may be optically separated from the otherwavelength emission peaks. Furthermore, these three lines in combinationallow a very broad temperature range to be detected. For lowtemperatures of about body temperature to well below freezingtemperature, the sharply changing intensity of the 5140 angstrom line asa function of temperature in this range is ratioed with either of theother lines whose intensity remain essentially the same in this range.For a medium temperature range of from about body temperature to 150°C., the 5379 angstrom line (steep variation) is ratioed with the 6280angstrom line (essentially flat). For a high temperature range of about150° C. to 300° C., the same two lines are used as in the medium rangeexcept here the intensity of the 5379 angstrom line changes rapidly as afunction of temperature while the 6280 angstrom line intensity remainsmore nearly constant over the high range.

A single instrument capable of operating with various phosphor sensorsover the entire range preferably is capable of measuring the intensitiesof all the above lines and selectively ratioing various pairs dependingupon the temperature range of operation. Of course, the particular formof the phosphor temperature sensor utilized for any particularmeasurement depends upon the object or environment being measured andthe temperature range. Several such sensors are described hereinafter.

Referring to FIG. 3, the intensities of two spectral lines foreuropium-doped gadolinium oxysulfide (Gd₂ O₂ S:Eu) as a function oftemperature of the phosphor are shown as emission lines 55 (at 4680angstroms) and 56 (at 5379 angstroms). In this phosphor material, 0.1atom percent of europium has been substituted for gadolinium.

The intensity of the 4680 angstrom emission line of europium-dopedyttrium oxysulfide (Y₂ O₂ S:Eu) is shown by curve 57 of FIG. 3, where0.1 atom percent of europium has been substituted for yttrium. Theintensity of the 5379 angstrom of the Y₂ O₂ S:Eu line is shown by curve58. Another line useful for referencing (ratioing) in Y₂ O₂ S:Eu is the6157 angstrom line represented by curve 59. This line has a temperaturedependence similar to the 6280 angstrom line. The curves 55, 56, 57 and58 show usable temperature dependent emission intensity characteristicsin different temperature ranges than those spanned by the lanthanummaterial exhibiting curves 51 and 52. These additional oxysulfidematerials are most usable over the rapidly changing portions of theircurves when referenced to a line such as the 6157 angstrom line. Thedifferences with useful temperature ranges of these materials aresignificant when selecting an optimum material for a specificapplication. The 5140 angstrom line or the 4680 angstrom line 55 ofgadolinium oxysulfide, for example, have particular advantages formedical temperature measurement since especially rapid changes occurwith good signal strength over the range of human body temperatures.

It will be noted from FIG. 3 that each of the gadolinium, lanthanum andyttrium oxysulfide materials illustrated has the same doping, namely 0.1atom percent of europium. However, experiments with materials of widelydifferent doping levels of europium indicate that the temperaturedependence are not significantly affected by doping level althoughabsolute values of the ratios of emission line intensities are affected.Hence, it is important to calibrate the temperature measuring instrumentfor the particular phosphor composition employed. The temperaturecharacteristics of the material are, as can be seen, very dependent uponthe phosphor host material, as well as on the choice of activator ion,thus permitting optimization of the temperature characteristics for aparticular application by selection of the proper host material.

Referring to FIG. 3A, a typical light intensity output characteristic isillustrated for the rare earth oxysulfide phosphors discussed above.This spectrum is for europium activated lanthanum oxysulfide and is theemission intensity at a particular wavelength line, as a function ofwavelength of the radiation exciting the phosphor. It can be seen thatthe most intensity is obtained when the phosphor is excited withultraviolet radiation. Ultraviolet radiation is preferred, therefore,for exciting the phosphor in most cases. But some optical systems thatmight be used to transmit exciting radiation have considerable losses toultraviolet radiation when compared to losses in the visible range. Along length of optical fiber, such as one over 100 meters in lengthmight be such a system. When the losses are great enough, it may bepreferable to excite the phosphor with visible radiation, such as ateither the blue or green excitation bands shown on FIG. 3A. Even thoughthe resulting excitation efficiency may be lower for visible thanultraviolet radiation, the improved visible transmission of a longoptical fiber can make up for this difference.

In order to adequately detect and measure these spectral line ratioswithout interference from adjacent emission lines, the fluorescentradiation 41 and 81 of FIG. 1 must first be passed, as part of the block100, through an optical filter such as a monochromator or interferencefilter set chosen to isolate the selected wavelength ranges in which thespectral lines of interest fall. It can be seen from the characteristicsof the phosphor illustrated in FIG. 2 that for the 4680 angstrom, 5861angstrom and 6157 angstrom lines, a filter having a bandpass of theorder of 50 angstroms is adequate for separation.

In addition to separation, it may also be desirable to correct themeasured line intensities within the block 100 for any strong backgroundradiation which may be present, such as that from room light or daylight. For that purpose, it may be desirable in certain circumstances toadditionally measure the intensity of radiation as seen through theutilized monochromator of filter when tuned to a spectral region nearthe fluorescent lines but where no fluorescent radiation is expected. Anexample using the phosphor whose characteristics are illustrated in FIG.2 is in the region of from 6000 to 6100 angstroms. Alternatively, thebackground can be determined by turning off or blocking the excitationsource and looking through the two filters. Any background radiation someasured can then be subtracted from the 5861 and 6157 angstrom lineintensities that are measured to yield a more correct ratio fortemperature measurement purposes.

A physical mixture of phosphor compounds can also be utilized, as analternative, in order to obtain desired temperature characteristics. Theintensity of one emission line from one compound of the mixture, forinstance, can be compared with the line intensity of another compound inorder to provide optimum measuring characteristics over a giventemperature range. Alternatively, two emission lines from each of twophosphor compositions can be utilized, the lines from one compoundcompared over one temperature range and the lines from the othercompound being compared over an adjacent temperature range. For example,a terbium doped lanthanum, gadolinium or yttrium oxysulfide may be usedas one compound in combination with an europium-doped lanthanum,gadolinium or yttrium oxysulfide as the other compound. Another usefulmixture might involve europium activated yttrium or gadolinium oxidemixed with one of the terbium activated oxysulfides mentioned above.

The phosphor materials mentioned above have the advantage of beingrelatively inert and stable. The emission lines of the phosphor are inthe visible or near visible region and thus transmission through longair paths, through water and other liquids, or through long opticalfibers, or through glass or quartz optics, is possible. Such a phosphordiffers from more conventional phosphors in that it emits very sharpfluorescent lines which can be readily optically isolated from eachother, and the temperature dependence of line intensities at aparticular wavelength is very strong relative to that at otherwavelengths over a given temperature range of practical interest. Otherphosphor materials having these characteristics can be utilized as partof the technique and structure of the various aspects of the presentinvention, as well.

Another form of phosphor having further different emissioncharacteristics is a single host compound containing two differentactivator elements. An example is uranyl molybdate activated witheuropium, a phosphor having two activators, triply charged europium(Eu³⁺) and the uranyl ion. The various combinations of the particularrare earth phosphors described previously by way of example arenumerous, thus providing a wide range of chemical, physical andradiation emission characteristics for different applications. Theflexibility of these techniques is therefore much greater than describedsince many other phosphors are also available and useful for temperaturemeasurement applications.

Phosphor compounds are usually thought of as solids because that is themost practical form, but they may also be in the liquid or gaseous stateif appropriate for different types of temperature measurement. Many ofthe activators discussed above may be dissolved in an organic liquid orsolid, thus also preserving the advantage of being useable inelectrically hostile environments. As an example of a liquid compound, atriply charged europium (Eu³⁺) ion (1 wt.%) in polyphosphoric acid withadded fluorescein (0.02 wt.%) emits a complex spectrum with separablefluorescence lines each rising from substantially zero to a peak andback to substantially zero again in less than 500 angstroms bandwidth,these lines having emission intensity that independently vary as afunction of temperature of the liquid. The intensity of two such linescan be detected and ratioed as discussed elsewhere herein to measureliquid temperature. The particular phosphors identified in this and thepreceding paragraph are discussed in some detail in an English languagepaper distributed by the Plenum Publishing Corporation and dated 1979,stated to be translated from a Russian article by N. N. Morozov entitled"Rare Earth Thermochromic Phosphors" appearing in Izvestiya AkademiiNauk SSSR, Neorganicheskie Materialy, Vol. 15, No. 1, pp. 153-156,January, 1979.

Another variation of the techniques described herein is to provide aphosphor temperature sensor that can measure temperature on a cellularor molecular level. The temperature dependent fluorescence ion ischemically attached to a molecule whose temperature is to be measured asin fluorescent "tagging". An application of this is where thetemperature of specific molecules reacting in a solution is desired tobe monitored independent of the overall temperature of the solution.Tagged molecules in solution can be excited and the emitted radiationdetected and processed as discussed elsewhere herein.

Remote Non-Contact Surface Temperature Measurements

Referring to FIG. 4, an object 21 within an environment 2 has itsoutside surface painted with phosphor material 46. By monitoring theemission of the phosphor, when properly excited, the surface temperatureof the object 21 can be monitored from a remote distance and withoutcontacting the object 21.

In the particular example shown in FIG. 4, the object 21 is anaerodynamic model positioned in an environment 2 that is a test windtunnel. The surface temperature being monitored on the model 21 providesinformation as to the effect of the air flow in heating the modelsurface.

The phosphor painted on the surface of the model 21 is excited toluminescence by illumination from ultraviolet lamps 62 and 63. In somesituations, an ultraviolet laser might be used as well, particularly formeasurement of selected object points. The ultraviolet output of thelamps 62 and 63 are passed, respectively, through windows 64 and 65 thatare transparent to ultraviolet energy so that it might pass into thewind tunnel 2 and onto the model 21. Another window 82 permits emittedradiation from the phosphor on the surface of the model 21 to begathered by an optical system, represented by lenses 83 and 84. Thecollected radiation 85 is then directed onto a filter and detectorsystem 103. The filter and detector 103 is similar to the filter anddetector 100 previously described with respect to FIG. 1.

Referring to FIG. 5, details of one form of the filter and detector 103are illustrated. A filter wheel 104 is positioned in the path of theradiation 85 from the phosphor. The wheel 104 has at least two differentfilters 105 and 106 spaced on different areas of the wheel 104 so thatas it is rotated by the motor 112 the filters 105 and 106 arealternately passed through the beam 85. The filters 105 and 106 aredesigned to be narrow bandpass filters to select out two differentspectral lines of the phosphor being utilized.

The two selected phosphor emission lines are thus applied in timesequence to a detector 107 whose output is applied to an electroniccircuit 108. The detector could be a photomultiplier or a siliconphoto-diode which would give only an average of the intensity of theparticular selected lines over the entire object 21 or the detector 107could be some other device, such as an image dissector or a televisioncamera, that would convert the optical image of the object 21 as viewedby the selected emission lines into a two dimensional intensity plot.The use of the latter type detectors has an advantage of permittingtemperature detection on each point of the object 21 separately. Theelectronics 108 receives a synchronous signal from the detector 111which tells it which of the two filters 105 and 106 are in front of thedetector 107 at any instant. This permits the electronics 108 to developthe two signals 109 and 110 representative, respectively, of theintensities of the two selected emission lines of the phosphor.

FIG. 6 shows another form of the filter and detector 103 of FIG. 4. Inthe form of FIG. 6, a beam splitter or dichroic mirror 90 is positionedin the path of the phosphor fluorescent emission beam 85 so that knownfractions of the intensity of the beam go in each of two directions. Onedirection is through a filter 115 and onto a single detector 116 todevelop an electrical signal 110'. The other path is through a filter113 onto a second detector 114 to develop a signal 109'. Each of thefilters 113 and 115 are selected to permit one or the other of twoselected emission spectral lines to pass therethrough and onto theirrespective detectors. The output signals in the lines 109 and 110 ofFIGS. 4 and 5, and 109' and 110' of FIG. 6, are applied to appropriatesignal processing and readout circuits as described with respect toblocks 120 and 140 of FIG. 1. The read-out device would depend, ofcourse, upon the type of detector used, being a television displaysystem or video storage medium if the detector 107 is a televisioncamera.

Remote Point Temperature Measurement

There are many applications of large machinery and apparatus wherein itis desired to monitor the temperature at one or more points within theapparatus while it is operating. Large machinery is especiallyexpensive. It is very inconvenient and expensive when it breaks down dueto local overheating. If such local overheating can be detected beforeany damage is done, then the cause of it can be determined, thusavoiding more costly shutdowns of the equipment. Monitoring the overallor average temperature of the equipment, by monitoring the temperatureof water or coolant, for instance, does not provide the necessaryinformation in most instances because the overheating could be raisingthe temperature of a small part of the machinery to an excessive anddamaging level without raising the average temperature any detectableamount.

One such piece of equipment wherein there has been a long need for suchpoint temperature measurement is in power transformers, some of whichare capable of handling several megawatts of electrical power.Destruction of such a large piece of equipment is not only extremelycostly but can significantly disrupt a large portion of an electricpower distribution system. The problem has not been satisfactorilysolved before since high voltage transformers and other high voltageelectrical equipment, cannot tolerate electrical sensors and conductorswithin the equipment. The oscillating fields generate currents, noisesignals and spurious heating in such conductors. In addition, theconductors provide a mechanism for producing disastrous short circuits.There is thus a need for a non-metallic temperature sensor that can beused inside of electrical power transformers and other types ofelectrical equipment.

Referring to FIG. 7, such a transformer is very generally illustrated.An outer shell 7 contains a transformer core 6 having windings 4 and 5therearound. The entire core and windings are submersed in an oil bath 3for insulation and cooling. In order to monitor the temperature of agiven spot on the interior of such a transformer, a single sensor 22 isprovided in accordance with another aspect of the present invention. Thesensor 22 is connected to one end of an optical fiber bundle 86. Thesensor 22 may be constructed without any metal parts at all and isoptically connected by the fiber bundle 86 to an appropriate filter anddetector system 100', an electric signal processing circuit 120' and adirect temperature read-out device 140'.

Referring to FIG. 8, the temperature sensor 22 is shown in cross sectionwherein it contains a phosphor material 47 in optical communication withone end of the optical fiber bundle 86. This end of the optical fiberand the phosphor form a probe which may be inserted into a transformeror other machinery. The probe is subjected to the temperature to bemeasured and the phosphor, being part of that probe, responds asdescribed hereinbefore with relative changes in the intensity of itsspectral output lines as a function of temperature.

The output of the phosphor 47 is obtained at an opposite end of thefiber bundle 86 by a lens 87 which directs the emission radiationthrough a beam splitter or dichroic mirror 88, through another lens 89,and thence to a system already described with respect to FIG. 6,including a beam splitter or dichroic mirror 90, two filters 113 and 115and two radiation detectors 114 and 116.

In order to excite the phosphor 47 to emit the desired lines, theembodiment of FIG. 8 employs an ultraviolet light source 66 whose outputis directed by a lens 67, passed through a broadband ultraviolet filter68 which blocks all but the ultraviolet light and then onto the beamsplitter or dichroic mirror 88. The element 88, if dichroic, is designedto transmit visible light but reflect ultraviolet light so that theoptical configuration shown in FIG. 8 utilizes such a characteristic toadvantage. The ultraviolet radiation is reflected by the element 88,directed through the lens 87 into the optical fiber bundle 86 andtransmitted through it to the phosphor material 47 to excite itsluminescent emission which provides the temperature information in acoded form, as described above.

Ultraviolet excitation can be employed with optical fibers when thefiber is less than 100 meters or so in length because of relativelystrong absorption or scattering of ultraviolet radiation by the fiberitself. Further, the level of ultraviolet radiation reaching thephosphor is preferably less than that level which drives the phosphorinto saturation. If below this level, the temperature dependent phosphoremission is independent of the intensity of excitation radiation, thusadvantageously eliminating a variable that would otherwise affectinterpretation of the temperature information.

It has been found that a tungsten-hologen lamp may be used for the lightsource 66 of FIG. 8, rather than more conventional sources ofultraviolet radiation. This source has the advantage that its output inthe ultraviolet range is adequate and yet small enough to maintain thephosphor excitation level below saturation, although the largeintensities present at longer wavelengths must be filtered out. Such alamp has the further advantages of being small in size, inexpensive,readily available in small power ratings, easy to control, andrelatively low in heat disipation. Such a lamp is therefore especiallyadvantageous for small and/or portable instruments and short fibers.

Referring to FIG. 8A, a modification of the system of FIG. 8 is shownwherein a probe 27 of a type similar to probe 22 of FIG. 8 is excited byconnection through a fiber optic 86' to an excitation source 60'. Theradiation from the phosphor within the probe 27 is carried by a separatefiber optic 86" to the appropriate filters and detectors 100". The fiberoptics 86' and 86" may be a single optical fiber each, or may be abundle of fibers. The use of the separate fiber optics 86' and 86" has aprincipal advantage of providing optical isolation between the phosphorexcitation radiation and radiation given off by the phosphor. Excitationradiation as well as possible low level fluoresence from the opticalfiber itself is thus kept clear of the detector 100". The result is lessoptical background noise and improved accuracy. The excitation source60' and detector 100" may also be more easily physically isolated usingthe bifurcation scheme.

Another advantage of these remote temperature measurement techniquesover more conventional thermocouple techniques is that the phosphorsensor may be remotely tested to assure that the temperature sensor isworking satisfactorily. This can be done by periodically obtaining theemission spectrum of the phosphor. If no expected lines are absent andif no new emissions are present, then it is confirmed that no chemicalor other change has taken place and that the sensor is in proper workingorder. This fail-safe feature could be of particular importance innuclear reactor systems.

FIG. 9 shows a variation of the probe and detecting system of FIG. 8wherein a probe 23 includes a phosphor material 48 attached to one endof an optical fiber bundle 91. Encapsulated within the probe 23 in thisembodiment is a radioactive material 69 which is selected to excite, fora period of time dependent upon the half-life of the material 69, thephosphor material 48. The emission of the phosphor material 48 istransmitted through the optical fiber bundle 91, through a lens 92 andonto a beam splitter, filter and detector system as described previouslywith respect to FIGS. 6 and 8. The radioactive material 69, used inplace of the ultraviolet source 66 of FIG. 8, may be, for example, anisotope of nickel, such as ₆₃ Ni, having a half life of 92 years. Thismaterial emits electrons but does not emit gamma rays. This probe 23 andcommunicating optical fiber bundle 91 still may maintain the desirablecharacteristic of having no metallic component if the ₆₃ Ni is in theform of an oxide or other non-metallic compound.

FIG. 10 shows a variation of either of the probe assemblies of FIG. 8 or9 wherein a single optical fiber bundle 92 provides opticalcommunication with a plurality of separate probes, such as the probes24, 25 and 26, which can be positioned at different locations within apower transformer or other apparatus. At one end of the optical fiberbundle 92, a few of the fibers are connected with each of the individualprobes 24, 25 and 26. At the opposite end of the fiber bundle 92, theopposite ends of the same optical fibers are connected to individualfilters and detectors. That is, the probe 24 is in optical communicationwith only the filter and detector block 117, the probe 25 only with thefilter and detector block 118, and so forth. Each of the assemblies 117,118 and 119 contains a complete and independent optical source, filterand detector system sufficient to generate and present output signalsfor the two wavelengths of interest to a common electronic processor 122which in turn obtains the ratio. Alternately, each of the blocks 117,118 and 119 can obtain the ratio and transmit to the processor 122 onlythe ratio signals. In either case, the processor preferably utilizescommon processing circuitry to sample the signals from the blocks 117,118 and 119 and apply these samples to a temperature display 141, ratherthan independently processing each signal with separate dedicatedcircuitry.

A variation of the multiple probe system of FIG. 10 is shown in FIG. 10Awherein a time division multiplexing technique is employed. Multiplexingof signals from separate temperature sensors has the significantadvantage of permitting a single instrument package to be utilized withmany sensors. Referring to FIG. 10A, temperature sensors 24', 25' and26' are connected through separate radiation transmission optical fibers401, 404, and 406, respectively, to individual dedicated detectorassemblies 409, 411 and 413. A source of excitation radiation 407 andappropriate optical system direct ultraviolet or other excitingradiation along optical fibers 402, 403 and 405 which are connected attheir opposite ends respectively to the temperature probes 24', 25' and26'. Each of the detecting stations 409, 411 and 413 is designed withappropriate filters to independently detect the intensity of radiationreceived from its respective probe within the two narrow radiation bandsof interest. This may be accomplished, for example, by the optical anddetector arrangements of FIGS. 5, 6 or 8. The electrical outputs of thedetecting stations 409, 411 and 413, proportional to the intensity ofradiation within the two wave-length bands from each of their respectiveprobes, are applied to an electronic circuit 415 which determines theratio of intensities from each probe, and thereby their temperatures.The signal output of the electronics 415 is applied to a temperaturedisplay 417 which indicates the temperatures of each of the temperatureprobes 24', 25' and 26'. The electronic circuit 15 includes anappropriate electronic switch that alternately connects to the signalline outputs of the detecting stations 409, 411 and 413, in timesequence. This permits a common electronic processing circuit to handlethe signal processing necessary from all three temperature probes.

As an alternate to the system of FIG. 10A, the common ultraviolet source407 and the respective separate optical phosphor exciting fibers 402,403 and 405 may be omitted. In their places, a beam splitter can beemployed at the end of each of the radiation receiving fibers 401, 404and 406 as part of their respective detecting stations, corresponding tothe beam splitter 88 of FIG. 8. As in that embodiment, a source ofultraviolet light could then be optically directed to each beamsplitter, so that the same optical fibers are utilized for excitation ofthe phosphor and for transmitting radiation from the phosphor back tothe detecting station.

The electronic circuits 415 can include as complicated and advancedsignal processing equipment as desired. For example, a digital datastorage system may be employed that allows sampling, integration anddisplay of the data from any of the probes, allowing the data to bebuilt up to whatever depth is desired in terms of a signal-to-noiseratio.

Alternatively, the separate probes can be scanned at the output end ofthe fiber optic bundle by a single detector station in a controlled andpredetermined fashion, as shown in FIG. 10B. A single detector assembly414 is positioned for being optically connected in sequence, one at atime, to ends of optical fibers 401', 404' and 406'. Such an opticalcoupling is provided in this specific example by a hexagon-shaped mirrorassembly 421 that rotates about its axis. Each mirror surfacealternately optically connects the detecting station 419 with each ofthe optical fiber ends, so that an output signal applied to anelectronic circuit 425 may be appropriately processed in order todisplay all three temperature signals on an appropriate display 427. Arotary position sensor 423 emits an electrical signal which is alsoutilized by the electronic circuits 425, as an indication of position ofthe mirror assembly 421. This position signal then tells the electronics425 which of the optical fibers 401', 404' or 406 which is opticallycoupled by a mirror surface to the detector station 414. The detectingassembly 414 may be of the type described previously employing twoseparate detectors and appropriate filters for directing each of thephosphor output lines to a separate detector.

A means for exciting the phosphor of the temperature probes is notillustrated in FIG. 10B, but may be one of several previously describedtypes. If radiation must be sent down an optical fiber to the probe end,it may be done so in a manner illustrated in FIG. 10A, wherein a commonultraviolet source 407 is employed. Alternately, each of the fibers401', 404' and 406' may be provided with a beam splitter which allowsthe ultraviolet energy to be sent down the same fiber or fiberstransmitting the radiation emitted from the phosphor back to thedetecting station. A preferable arrangement, however, would be to use asingle ultraviolet source that is positioned with respect to thedetecting station 414 of FIG. 10B which uses the mirror assembly 421 toalternately send ultraviolet radiation into the end of the optical fiberto which the detector at that instant is being optically coupled. Thishas an advantage of requiring less ultraviolet radiation power, sinceonly one phosphor probe would be illuminated at any one time, ratherthan all probes.

The single detecting station embodiment of FIG. 10B has the advantage ofeliminating any variation between channels which might be due todifferent detector characteristics in a multi-detector array. On theother hand, the multi-detector approach of FIG. 10A has the advantage ofnot requiring any moving optical parts and allowing data to beaccumulating from all probes all the time. In each of these embodiments,of course, a different number of temperature sensing probes may beemployed other than the three chosen for illustrative purposes. In thecommon detecting station embodiment of FIG. 10B, each of the probesutilized with it must have the same phosphor characteristics, so thatthey they can all work with a common detecting station 414.

FIG. 10C shows a variation of the optical scanner of FIG. 10B. A mirrorsystem 421' is rotated about an axis 418 by a motor 420. Mirrors 422 and424 are held within the rotating housing 426 at a 45° angle with theaxis 418. A lens 428 is mounted in the rotating housing for scanning intime sequence a plurality of optical fiber ends, such as the fiber 401"shown. The mirror system thus presents light signals in time sequencefrom a plurality of optical fibers to a common position along the axis418 to be detected by the detector 419'. The motor 420 is preferably astepper motor that rotates the system 421' from one optical fiber to thenext after holding the assembly 421' fixed on each optical fiber for aselected signal integration time. This avoids wastage of measurementtime between detectors as would be the case with a continuously rotatingsystem.

Frequency multiplexing techniques may alternatively be employed. Theoptical signal from each sensor may be chopped (modulated) at a uniquefrequency and all converted to electrical signals by illuminating acommon detector. The phosphor emission electrical signals from thedetector are then separated by appropriate electronic filtering ordemodulation techniques according to the unique carrier frequency ofeach probe.

Obviously, the specific types of equipment where such multipletemperature probes have utility are numerous. An electric powergenerating nuclear reactor is an example of a system where the inventioncan be used with great advantage to measure temperature of remote,inaccessible positions. Various industrial processing or manufacturingplants also can utilize these techniques with advantage.

Moving Objects or Materials

The techniques of the present invention lend themselves to opticalcommutation regardless of the specific type of phosphor utilized. Theymay be applied without physical contact and are immune to electricalnoise. A specific application of optical commutation is on a rotatingdevice 200 as shown in FIG. 11. This device could be a motor, turbine orgenerator. The phosphor containing probe 22 is embedded in the rotatingpart 200 as are an optical fiber input bundle 201 and an output bundle203. The optical fiber bundles terminate at an external circumference ofthe wheel or rotating part 200. This permits the non-rotatable fixedpositioning of an exciting radiation source, such as an ultravioletsource 205, and phosphor emission receiving optics 207 adjacent thereto.At one position, for a short distance, in each rotation of the rotatingpart 200, the ultraviolet source and the phosphor emission radiationoptics 207 will be aligned with their respective optical fiber bundles201 and 203. At that instant, the temperature of the part at theposition of the embedded phosphor containing probe 22 is measured. Theoptical system 208 is connected with an appropriate filter and detector209 of one of the types discussed with respect to other of theembodiments above.

The same technique can be utilized, as shown in FIG. 12, for a movingbelt 211. This optical temperature measurement technique can be seen tohave considerable advantages since no physical connection of wires orother devices are required between the moving part and the fixedmeasuring equipment. As an alternative to the particular opticaltechnique shown in FIGS. 11 and 12, the rotating part 200 and the belt211 could also be painted with a phosphor paint as discussed withrespect to FIG. 4.

It will be noted from FIGS. 11 and 12 that multiple sensors can beemployed to detect the temperature at different locations on the object.Optical fibers could then be connected to each of these additionalsensors in the manners shown in FIGS. 11 and 12, but terminated at theedge of the moving object at different locations. The detecting andilluminating stations would then in effect be operating in a timemultiplex mode, similar to that described previously with respect toFIGS. 10A and 10B.

Another alternative to what is shown in FIG. 11 is to position theoptical fibers to communicate over the gap at or very near the axis ofrotation of the rotating object. This has an advantage of increasing theduty cycle of temperature measurements.

Fluid Temperature Measurement

Referring to FIG. 13, yet another application of the basic concept ofthe present invention is shown wherein the temperature of a movingstream of fluid 215 passing through a pipe 217. A window 219 is providedin the wall of the pipe 217 and characterized by transmitting theexciting and emitted radiation without significant attentuation. Anappropriate exciting electromagnetic energy source 221 illuminates theinterior of the pipe through the window 219. The fluid stream 215 isprovided with a plurality of phosphor coated particles 223 that have asize and density consistent with the type of fluid 215 and flow to beexpected so that they remain distributed within the fluid stream 215.The radiation from the ultraviolet source 221 causes the phosphorcoating on the particles 223 to luminesce and this luminescence isgathered by an optical system 225 which collects and transmits thephosphor radiation to an appropriate detector 227. By detecting andratioing the intensities of two phosphor emission lines of interest, thetemperature of the fluid stream 215 is determined since the particleshave been given a chance to reach a temperature equilibrium with that ofthe fluid stream 215. Alternatively, but with some disadvantage, asingle phosphor emission bandwidth only may be detected withoutratioing, such as is possible with a conventional thermographicphosphor.

Each of the particles 223 is chemically inert, with regard to itsinteraction with the fluid in which it is used and also, of course, withthe phosphor material which is attached to it. Another arrangement isthe encapsulation of the phosphor within an optically transparent,chemically inert medium. For the embodiment of FIG. 13, it may alsodesirable, as shown, to provide a large number of particles to have adistribution of specific gravities so that they maintain a distributionthroughout the fluid stream 215, as shown.

Another particular application of the immersed bead technique is shownin FIG. 13A wherein a container 231 contains a body of liquid that isnot moving. Within the liquid are a plurality of beads 233. Thecontainer 231 could be a clinical laboratory cuvette, for example,wherein it is desired to maintain the liquid at a particular precisetemperature while monitoring a chemical reaction taking place. Thecontainer 231 illustrated in FIG. 13A should be optically clear at thewavelengths of light utilized so that exciting radiation may betransmitted to the beads 233 and the resulting luminescence transmittedback out to an appropriate detector, according to previous discussions.Alternatively, the specific gravity of the beads 233 may be made all thesame as that, rather than being distributed throughout the height of theliquid within the container 231, they are caused to all sink or allfloat to the top. This would have an advantage of allowing excitationand viewing of the luminescence radiation either from the above theliquid surface or from the bottom of the container.

Rather than solid temperature sensors, a liquid phosphor temperaturesensor may be added to the body of liquid whose temperature is to bemeasured. Such liquid temperature sensing material has previously beendescribed. It can be provided with a specific gravity relative to thatof the body of liquid to be measured so that it floats on top, sinks tothe bottom or is distributed throughout the liquid.

Further Sensor Configurations

A further application is illustrated in FIG. 14. The end of an opticalfiber bundle 301 is capped with a disposable temperature sensing sleeve303. The sleeve 303 is formed of a cylindrical base portion 305 that iscarried at the end of the optical fiber 301. One end of the cylindricalbase 305 is capped with a thin, heat conductive cap 307 such as, forexample, one made of metal. The cap 307 may, on the other hand, simplybe thin plastic as a unitary part of the cylindrical portion 305. Apreferable technique for forming a unitary cover 305/307 is by plasticinjection molding. On an inside surface of the cap 307 is a phosphorcoating 309. At the other end of the fiber optics 301 (not shown) is anexcitation source and detecting system of a type described earlier. Theend of the optic fiber 301 with the sleeve 305 is immersed in theenvironment for which a temperature is desired to be taken, such as ahuman or animal cavity, or liquid baths. If the cap portion 307 is notoptically opaque, then, if required, a coating of light blockingmaterial (not shown) may be placed on the outside of the probe cover 303over the portion 307 and along the base portion 305 far enough toprevent extraneous light from entering the optical fiber 301 andundesirably affecting the temperature measurement.

The advantage of the sleeve 303 is that it may be discarded after asingle use, thus preventing cross contamination from occurring insequential temperature measurements. The comparing or ratioing of thetwo wavelength band signals as described earlier permits sleeves to beinterchanged without having to re-calibrate the detector and displayinstrument between sleeves. A significant advantage of using the presentinvention for this type of measurement is that it has a very low thermalmass, resulting in the temperature indicating phosphor 309 reaching asteady state value of the temperature of its surroundings very quickly.It will also be noted that the phosphor 309 need not be held tightlyagainst the end of the optical fibers 301, since an air gap can betraversed by these techniques. Precise positioning of the probe cover onthe optical fibers 301 is thus unnecessary. The other advantagesdescribed above concerning the phosphor and optical fiber structuregenerally are present here as well. This technique is especially adaptedto be embodied as a clinical thermometer for use to measure thetemperature of patients in replacement of the slower electronicthermometers now becoming widely used in hospitals.

A closed end 306 of a modified probe cover 304 is shown in cross-sectionin FIG. 14A. The cover 304 is made as a single piece injection moldedplastic. A primary difference with the probe cover 303 is that the cover304 has no phosphor layer applied on its inside closed end surface.Rather, phosphor particles are contained in the plastic tip itself. Theend 306 must thus be substantially transparent to the exciting andemitted radiation between the inside of the cover 304 and the phosphorparticles embedded therein. A substantially light opaque coating 308 mayagain be provided on the outside of the cover 304, if necessary, inorder to prevent an undesireable level of optical radiation within ornear to the fluorescent emission bands being detected from entering theend of the fiber optics 301.

Yet another application utilizes the probe and optical fiber embodimentof the present invention implanted at one or more points within humansand animals. A potential application is illustrated in FIG. 15 wherein ahuman or animal body 311 contains a cancerous tumor schematically shownat 313. A technique presently being explored for treating cancer, calledinduced hyperthermia (heating), involves irradiating the tumor 313 bymeans of energy 315 from an ultrasonic or electromagnetic radiationsource 317, the result being induced heating. However, the success ofthis technique for treating the tumor 313 is dependent upon maintainingthe tumor at a specific, well controlled elevated temperature for aparticular time.

Therefore, a means of monitoring and controlling the temperature of thetumor 313 is to introduce surgically, with a hypodermic needle or via acatheter a small fiber optic temperature probe 319 of the type discussedwith respect to FIG. 9 above and FIG. 16 hereinafter. An optical fiber321 communicates between the temperature probe 319 and excitation anddetection apparatus 323. For this application, of course, the size ofthe temperature probe 319 and cross-sectional dimension of the opticalfiber 321 needs to be as small as possible. The optical fiber 321 can belimited to one or two fibers and the temperature probe 319 can be formedby coating the phosphor and a thin encapsulating material directly ontothe end of the optical fibers. The sensor end of a single optical fiberpreferred for implanting in humans is described with respect to FIG. 16hereinafter. The temperature of the tumor 313 can then be monitored andthe intensity of radiation from the source 317 adjusted to maintain theoptimum temperature for treatment. If heating of the tumor isaccomplished by radio frequency or microwave radiation, the opticalprobe is insensitive to directly induced heating or electrical noisepick-up by these fields. Such would not be the case with a moreconventional electrical metallic sensor system. The low thermal mass ofthe small fiber sensor assures that it will quickly assume thetemperature of its environment as that temperature changes. The fiberdoes not conduct heat so that the sensor does not draw heat away,changing the temperature. Being non-metallic, the sensor and fiber donot distort the heating pattern of the radiation field.

It is desired in hyperthermia cancer treatments that the temperaturearound the tumor 313 be monitored at a plurality of points, asillustrated in FIG. 15A. In that arrangement, a plurality of singleoptical fiber lengths 327, 329, 331 and 333 have their phosphor coatedends implanted within the patient in the area surrounding or within thetumor 313. Each of the lengths of optical fiber 327, 329, 331 and 333 ismade to be a maximum of a few meters long, and is constructed at itsfree end that is implanted in the patient according to view of FIG. 16.The opposite ends of these fiber lengths are connected by appropriatecommercially available optical connectors 335 to a detecting station.Nothing else need be provided along the optical fiber between its ends.One form of detection station that is applicable is described withrespect to FIG. 8 wherein the system there shown would be duplicated foreach of the optical temperature sensors 327, 329, 331 and 333. Since theexciting radiation is at a different wavelength than the fluorescentradiation, a single optical fiber can be used to transmit both. Thesingle fiber configuration allows a very small probe which is importantin human applications. In order to reduce the cost and complexity of thedetecting station, a multiplexing system along the lines of thatdescribed with respect to FIG. 10B or 10C may be preferable, utilizingthe version of those systems that transmit both the exciting and emittedradiation in opposite directions along the same optical fiber.

Each of the optical fiber sensors 327, 329, 331 and 333 are preferablyconstructed to be disposable, so that new, sterile optical fiber sensorsmay be implanted in each patient. For that reason, it is desired thatthey be inexpensive and easily connected and disconnected fromtemperature instrumentation through their connectors 335. Of course, alesser or greater number of temperature sensors may be utilized.Alternately, fiber sensors may be reused after sterilization, but inthis case also easily interchangability and permanency of calibrationare important.

The free end of each of the temperature sensing fibers 321, 327, 329,331 and 333 is indicated generally in FIG. 16. The fiber core 337 issurrounded by plastic cladding 339 which in turn is covered by an opaquesheath 338. The goal is to make the diameter of the overall structure assmall as possible for implanting in a patient. An overall diameter ofthe probe of less than 1 millimeter and preferably approximately 1/2millimeter is desirable.

A multi-sensor probe is shown in FIGS. 16A and 16B. Seven optical fiberswith cladding but without a sheathing are held together within a commonsheath 387, six fibers 381, 382, 383, 384, 385 and 386 surrounding acenter fiber 390. Each of these optical fibers is terminated at adifferent position along the length of the probe. For example, the fiber381 has a phosphor sensor 388 attached to it and another piece of fiber389 is positioned between the sensor 388 and the end of the probe tomaintain a uniform diameter. Each of the other outside optical fibers382, 383, 384, 385 and 386 is similarly terminated at a different andunique position along the length of the probe, thus obtaining atemperature profile therealong. The center optical fiber 390 can beinactive or alternatively have a phosphor sensor attached at its endnext to the sheath 387 at the extreme end of the probe. With currentoptical fiber technology, the probe can be made less than one millimeterin diameter. Of course, a greater or lesser number of optical fibers maybe employed but six surrounding a center optical fiber, where there areall of the same diameter, provides a very compact probe. The radiationemitted by the phosphor sensors is detected at the opposite ends of theindividual optical fibers according to one of the techniques discussedearlier for multiple sensors.

Referring again to FIG. 16, a spot of phosphor 341 is held by anappropriate binder to the end of the optical fiber core 337. Overlayingthe phosphor layer 341 is a reflecting layer 340 which in turn iscovered by an opaque layer 342 that prevents stray light frominadvertently entering the fiber 337 and interfering with the accuracyof the resulting temperature measurement. A physically tough protectivelayer 344 surrounds the end of the fiber and the temperature sensor.Preferred materials are: potassium silicate or silicone resin for thephosphor binder in the layer 341; titania in a silicone resin binder forthe reflecting layer 340; various transition metal oxides, such as thecombination of chromic oxide, copper oxide and molybdenum oxide sold byFerro Corporation as their V302 black pigment, mixed in a plastic orsilicone resin binder to form the light barrier layer 342; and a thinbut hardy plastic coating for the outer layer 344. This particularcombination avoids electrically conductive materials, particularlymetals and carbon black pigments, for applications in electrostatic orelectromagnetic fields.

Each of the temperature sensors in the probe of FIGS. 16A and 16B isformed in the manner described with respect to FIG. 16 except that theouter layer 344 is omitted from each. The probe of FIGS. 16A and 16Ballows a linear distribution of sensors to be positioned through anobject, such as a biological tumor, with a single probe, thus reducingthe number of needles or probes that need to be inserted. Thepositioning of two such multi-sensor probes at right angles to eachother allows the acquisition of two-dimensional temperature profiles.

While the cancer application of hyperthermia is currently of thegreatest interest, there are potentially various other applications forinduced heating in human or animal bodies as well. Sensors of the typesdescribed can also be used for other human temperature measuringpurposes, such as during surgery or in thermodilution catheters. And thestructure of FIGS. 16, 16A and 16B have a wide variety of non-medicalapplications as well.

Particular types of temperature dependent phosphor carriers which have awide variety of uses are illustrated in FIGS. 17, 18 and 19. Referringinitially to FIG. 17, a small piece of a substrate material 343 is thecarrier for a quantity of phosphor material 345 of the type discussedpreviously, which is held by a binder onto the surface of the substrate343. On an opposite surface of the substrate 343 is optionally providedan adhesive layer of material 347. The result is a convenienttemperature sensor 349 which can unobtrusively be applied to the surfaceof a container 351, as shown in FIG. 18, or other object whosetemperature is desired to be monitored. The size of the sensor 349 maybe small, if desired--e.g., one square inch or less.

The temperature sensor 349 is most easily formed as one of a largenumber in a sheet. A larger sheet of substrate material, such as Mylarplastic or a metal foil, can be perforated to permit tearing apartindividual sensors such as sensor 349. The phosphor and binder material,in liquid form, is coated onto one side of the sheet and allowed to dry.Likewise an adhesive is coated on to the backside of the same sheet,either before or after application of the phosphor. When the phosphorbinder dries, the sensor 349 is formed and the large sheet of suchsensors is then stored until use of one or more is desired, when theyare then removed in the same way as a postage stamp is removed from asheet of stamps. A protective layer for the adhesive 347, such as waxpaper, may alternatively be applied as well in order to preserve theadhesive until it is ready to be used, at which time the protectivelayer (not shown) is removed.

Such a sensor 349 when applied to the bottle 351 is excited and detectedin a manner shown briefly in FIG. 18 but described in more detailpreviously. A source 353 of radiation illuminates the phosphor on thesensor 349. The emitted radiation intensity within the desired bandwidthregions is detected by an assembly 355, in order to determine thetemperature of the phosphor and thus the temperature of the bottle 351with which the phosphor is in a heat conductive relationship.

Referring to FIG. 19, a modification of the sensor of FIG. 17 is shownwherein the substrate 356 is itself provided with the phosphor particlesembedded therein, as described with respect to the tip 306 of thetemperature probe 304 of FIG. 14A. The substrate 356 is thus preferablymade of an optically clear plastic material. An adhesive layer 357 isapplied to one side of the substrate and a protective layer 359 isattached to the adhesive, such as wax paper, for easy removal just priorto attachment of the temperature sensor to the object whose temperatureis to be monitored.

The temperature sensors of FIGS. 17 and 19 are easily manufacturable atlow cost in large quantities. They thus may be disposed of after asingle use. The phosphor material is conveniently placed very close toand in heat conductive relationship with the surface whose temperatureis to be measured. The applications of this technique are almostendless, one application being in a clinical laboratory where thetemperature of a test tube or other sample holding device needs to bemonitored in order to keep it within pre-determined limits while achemical reaction or biological growth is allowed to proceed. Foodprocessing is another application wherein food containers are heated,possibly by microwave radiation. The temperature sensor substrate may beremoved from the container after the processing is completed anddiscarded, no trace of the use of the temperature sensor being left onthe container. Or the sensor may be left in place permanently.

As discussed extensively previously, a preferred phosphor for theembodiments of FIGS. 14 through 19, and those discussed hereafter, isone characterized by radiation emission intensity variations inoptically separable bandwidths as a function of temperature that areindependent of one another so that a ratio or other comparison of theintensities gives the desired temperature indication. But thesephosphors or the more conventional thermographic phosphors can also beused, if desired, in these unique approaches to temperature measurementwithout the ratioing of two emission intensities. In such a case, theintensity of the entire emission spectrum of the phosphor, or of aportion of it, is a direct indication of temperature, with the addedrequirement that the user calibrate the detector instrument for varyingexcitation radiation intensities, optical path absorption, and similarchanges over time that the ratioing technique eliminates as concerns.Although it is more difficult to utilize the single bandwidth technique(the leval of excitation must be carefully controlled during aparticular temperature measurement and the device re-calibrated betweenmeasurements), there may be some applications where these disadvantagesmust be accepted. Even the monitoring of emission frequency shift, decaytime, or some other temperature dependent characteristics of phosphormay be utilized in the unique temperature sensor configurationsdisclosed herein.

Other Applications

The techniques of the present invention also have application for pointtemperature measurements in clinical, chemical, materials and foodprocessing systems. The advantage of an optical fiber and temperatureprobe system as described herein in such applications is that they arechemically inert, have a fast response time, provide electricalisolation, can be permanently calibrated, are of low cost, aresterilizable and can even be used in moving machinery. These sensors canalso be used to measure temperature of materials undergoing microwaveheating or curing, an application where a thermocouple or any othermetallic temperature measuring apparatus cannot be easily used forreasons discussed earlier.

A particular further application takes advantage of the fact that adirect physical contact need not be maintained with an object undermeasurement. In such applications, a dot of phosphor can be placed oneach package and the temperature thereof monitored by monitoring theemissions of the phosphor when excited in the manner discussed above. Aflexible plastic bag 361 is illustrated in FIG. 20 as having a phosphordot 363 affixed to a surface of the bag by an appropriate binder, oralternatively, the phosphor may be suspended in an optically clear bagwall. In one application the bag might contain food being processed.After processing, the food bag may be sold to the consumer of itscontents who may then throw the bag away.

Another of many such applications is illustrated in FIG. 20A. Acontainer, such as a small disposable plastic clinical laboratorycuvette 365, has a phosphor dot 367 printed directly thereon fortemperature monitoring of the container and its contents during clinicaltests. Such containers might be reused after washing and sterilization,in which case the integrity of the phosphor temperature sensor should bemaintained, or they might be discarded after each use. Such laboratorysample containers could also be plastic bags as discussed in connectionwith FIG. 20.

The optical fiber technique of the present invention permits pointtemperature measurements to be made at a distance from the detection andexcitation apparatus. The use of such techniques for monitoringtemperatures at various points in an industrial plant can easily involveoptical fiber runs in excess of 100 meters. For such long runs, it maybe preferable to use excitation radiation within the visible spectrumwith a rare earth phosphor acting as the temperature indicating device.The particular excitation radiation that would be sent down the longoptical fiber and the phosphor composition for such an application havebeen discussed earlier with respect to FIG. 3A. If conventional(non-rare earth) phosphors are used, many can be found which respond tovisible radiation.

The technique can also be broadly applied to imaging thermographywherein an object scene is imaged onto a phosphor screen and theemissions detected through filters by a television camera to measure therelative intensity of two emission lines and thence the temperature ofthe image, the latter being proportional to the temperature of theobject scene. In yet another approach to thermal imaging, the phosphorscreen could be mounted within a vacuum tube, illuminated from one sideby the thermal image, via a suitable infrared-transmitting window andsubstrate, and excited from the other side by an electron beam scannedin raster fashion. In this instance the thermal image could bereconstructed using a single pair of optical point detectors suitablyfiltered with the resultant line intensity ratio thence used to modulatethe intensity of the electron beam of a cathode ray display tube whichis also scanned in raster fashion in synchronism with the excitingelectron beam.

Special Probe Designs

The fiber optic probe configurations discussed previously are limited inthe upper temperature which they may be used to detect. This is becauseplastic materials that surround existing commercial optical fibers tendto degrade at temperatures above 150° C. to 200° C. When this happens,the result may be to reduce severely the light transmitting efficiencyof the fiber. Similarly, at very low temperatures the indices of thefiber and cladding may come to the same value and the optical fiberceases to act as a light pipe.

Referring to FIG. 21, a plastic-clad optical fiber 501 is shown incross-section. It includes a silica core 503 surrounded by a siliconecladding 505 and an outer sheath 507. When the fiber is bent or is underpressure, the cladding typically flows allowing the sheath to contactthe core with resultant loss of light upon sustained exposure totemperatures between 150° C. and 200° C. The sheath itself may melt ordegrade at temperatures in the vicinity of 200° C. Thus, for localizedhigher temperature (or very low temperature) measurements, the sheathand cladding are removed from a length of the optical fiber at its freeend. A phosphor temperature sensing material 509 of the type discussedpreviously is attached to an end of the fiber core 503. Encapsulatingthis phosphor and the end of the fiber is an opaque tip 511 that canwithstand high temperatures. Single crystalline NiO, Cr₂ O₃ or MnO₂ areexamples of possibly useful tip materials. The tip could alternativelybe of metal if the sensor is not to be used in an electromagneticallyhostile environment.

In order to surround the exposed core 503 with something having a lowerlight refractive index and the ability to block light from entering orleaving the core along that length, a cylindrically shaped silica spacer513 surrounds the core 503 in a manner so as to leave an air gap aroundthe core which provides the necessary difference of index of refractionat the surface of the core material 503. The core 503 is held straight,preventing any extraneous light from entering or leaving the core 503.An outer cylindrically shaped silica holder 515 provides over-allstructural rigidity. The materials at the end of the optical fiber arethus able to withstand temperatures of 300° C. and up. Conversely theprobe can also be used at very low temperatures where the optical fibermight not conduct light for the reasons discussed earlier.

Because the fiber core 503 and surrounding cylindrical sleeves are allmade of silica, the coefficient of expansion of the entire assembly isuniform. Silica is also inert so does not react with elements in thesurroundings. Silica further does not conduct heat readily so the probeof FIG. 21 will not drain heat from or conduct heat to the environmentbeing measured.

Because the tip 511 is of a different material than the silica elementsit contacts, the tip cannot be threaded or glued in place since itslikely different coefficient of expansion would break any suchconnection as the probe is heated and cooled. Therefore, the tip isconically shaped to be held in an opening at the end of the outercylindrical sleeve 515 in a manner that it cannot be moved out throughthat opening. The tip 511 is securely held against an inside of thesleeve 515 by an end of the inner sleeve (spacer) 513. The end of theoptical fiber core 503 containing a coating of phosphor 509 isfrictionally held within a cylindrically shaped hole provided in therear surface of the tip 511.

Another type of optical fiber uses a doped silica coating over a puresilica core in order to provide a self-cladded structure. However, athin, organic buffer layer, typically an epoxy, is applied to an outersurface of the cladding to protect the fiber from oxidation and surfacescratching which would lead to fiber breakage. This organic buffer isalso unable to withstand temperatures of 200° C. and thus the probestructure of FIG. 21 can also be used to advantage with that type ofexisting optical fiber, modified to adapt to a fiber without the thicksheath 507 of the FIG. 21 plastic-clad optical fiber. The probe of FIG.21 is very small in size, because it surrounds a single optical fiberand thus has all of the advantages discussed previously of small,unobtrusive temperature sensors. The thermally conducting tip 511 ismade to be extremely small and is surrounded by thermally non-conductingmaterials.

Another special application temperature sensor is illustrated in FIGS.22 and 22A for contacting moving materials or machinery whosetemperature is desired to be detected. This sensor is based upon theadvantage of the present invention wherein transmission of temperaturedata is possible across a physical gap in the optical system, asdiscussed previously. There are applications wherein the temperature ofan object moving with respect to the temperature measuring station is tobe detected. The rotating probe of FIGS. 22 and 22A is especiallyadapted for contacting and measuring the temperature of moving wire,synthetic fiber, yarn, fabric, and similar items.

Referring to FIGS. 22 and 22A, a handle 521 is connected to an end of aprobe shaft 523. Connected to another end of the probe shaft 523 is arotating wheel 525. The roller 525 is rotatably held at the other end ofthe shaft 523 by bearings 527 and 529. A shroud 531 is attached to theshaft 523 and surrounds the wheel 525 in order to minimize convectivecooling of the wheel.

An optical fiber 533 is carried within the shaft 523 along its entirelength. An end portion 535 of the optical fiber 533 emerges from theshaft 523 within the wheel 525. The interior of the wheel 525 is hollowand shielded from exterior light. The optical fiber end 535 is heldfixed to the shaft 523. The open interior of the wheel 525 is blockedfrom communicating with the outside around its circumference only by athin metal strip 537 that extends completely around the outercircumference of the wheel. On its inside surface, the metal strip 537is coated with a temperature sensitive phosphor, preferably of the typediscussed previously. As the wheel 525 spins with respect to the shaft523, the phosphor coated on the inside of the metal strip 537 passescontinuously at close proximity to the extreme end of the optical fiber535. The phosphor is illuminated by exciting radiation from the fiber.The fiber receives the fluorescent emission from the phosphor strip andreturns it to an instrument for analysis and interpretation of thetemperature as discussed previously.

Wire, fiber, yarn, and similar items whose temperature is to be measuredmay be drawn over the wheel within its outer circumferential groove incontact with the metal plate 537. As an example, the fiber or yarn maybe being heated prior to processing. In this case, the rotating probewould provide a station for measuring and controlling fiber temperaturewhile the fiber itself is moving rapidly. As another example, therotating probe may itself be moved along an electrical transmission linefor purposes of measuring heating and detecting resistive segments.However employed, the metal strip and phosphor layer are heated to theapproximate temperature of the item in contact with the rotating probe.This temperature may then optically be determined from a remotedetecting station along the optical fiber 533 according to one of thetechniques described previously. This temperature sensing technique hasan advantage of creating little or no friction with the article to bemeasured. The temperature measurement is therefore not altered byfrictionally created heat.

The same type of instrument can advantageously be used for measuring thetemperature of moving flat surfaces or rotating drums. For thatapplication, there would be no concave groove in the outer circumferenceof the wheel 525 as shown in FIG. 22A, but rather the outside surface ismade to be flat or slightly convex in order to make a good thermalcontact between the circumferential thin metal piece and the surface ofthe article whose temperature is to be measured.

Other particular applications will become apparent from thisdescription. Although the various aspects of the present invention havebeen described with respect to preferred embodiments thereof, it will beunderstood that the invention is entitled to protection within the fullscope of the appended claims.

I claim:
 1. For a temperature measuring system having a visible ornear-visible electromagnetic radiation detector optically coupled to oneend of at least one optical fiber for receiving radiation from said onefiber that is indicative of temperature, a radiation emittingtemperature sensor, comprising:a carrier shaped for removable attachmentto another end of said at least one optical fiber and adapted to bepositioned in heat conductive relationship with an environment whosetemperature is to be measured, and a quantity of phosphor materialattached to said carrier in a position to emit radiation that isviewable by said detector at said at one end of said at least one oneoptical fiber when said carrier is attached to said another end, saidphosphor material being characterized by emitting, when excited,detectable optical radiation that varies as a known function of thephosphor material temperature.
 2. The temperature sensor according toclaim 1 wherein said carrier includes an elongated hollow member open atone end to receive said at least one optical fiber and closed at anotherend, said phosphor material being carried by said hollow member at itssaid another end.
 3. The temperature sensor according to claim 2 whereinsaid carrier is especially adapted for clinical thermometer use and isdisposable.
 4. The temperature sensor according to any of claims 1, 2,or 3 wherein said carrier is a heat conducting substrate and saidphosphor material is coated onto a surface of said substrate.
 5. Thetemperature sensor according to any of claims 1, 2, or 3 wherein saidcarrier is a medium that is optically transparent in at least a portionthereof to which said phosphor material is attached, and further whereinsaid phosphor material is carried within said medium.
 6. The temperaturesensor according to claim 1 wherein said carrier is especially adaptedfor clinical thermometer use and is disposable.
 7. The temperaturesensor according to any of claims 1, 2, 3 or 6 wherein the emittedradiation of said phosphor is additionally characterized by havingrelative intensities within two optically isolatable bandwidths thatvary as a known function of the phosphor temperature.
 8. A temperatureprobe sleeve, comprising:an elongated hollow member being open at oneend and enclosed at another end, said open end of the member beingconfigured to receive an optical fiber therethrough, and a layer ofphosphor material held in immediate physical contact with said anotherend of said hollow member, the phosphor material being characterized byemitting, when excited from a remote source, detectable opticalradiation that varies as a known function of the phosphor temperature,whereby said sleeve is positionable on an end of an optical fiber totransmit the exciting radiation to said phosphor and transmit phosphoremissions along said fiber for the purposes of determining temperaturesof the surroundings of said enclosed hollow member end.
 9. The probesleeve according to claim 8 which additionally comprises a layer ofopaque material at said another end on its outside surface, wherebyextraneous light is prevented from entering the optical fiber when thecover is used for temperature measurement.
 10. The probe sleeveaccording to claim 8 wherein said hollow member is especially adaptedfor clinical thermometer use and is disposable.
 11. The combinationaccording to any of claims 1, 2, 8, 9 or 10 wherein said phosphor isadditionally characterized by emitting, when excited, electromagneticradiation within optically isolatable bandwidths at at least twodistinct wavelength ranges and with relative intensities therein thatvary as a known function of the phosphor temperature.
 12. Thecombination according to any of claims 1, 2, 3, 8, 9 or 10 wherein saidphosphor is additionally characterized by emitting, when excited, atleast two non-overlapping optical sharp spectral lines of radiation thateach rise from substantially zero emission to a peak in less than 100angstroms bandwidth.
 13. The combination according to any of claims 1,2, 3, 8, 9 or 10 wherein said phosphor comprises a composition (RE)₂ O₂S:X wherein RE is an element selected from the group consisting oflanthanum, gadolinium and yttrium, and wherein X is a doping elementwith a concentration of from 0.01 to 10.0 atom percent and is selectedfrom the group consisting of europium, terbium, praseodymium, samarium,dysprosium, holmium, erbium and thulium.
 14. The combination accordingto any of claims 1, 2, 3, 8, 9 or 10 wherein said phosphor comprises acomposition (RE)₂ O₂ S:X wherein RE is an element selected from thegroup consisting of lanthanum, gadolinium and yttrium, and wherein X isone or more activators with a concentration of from 0.01 to 10.0 atompercent and is selected from the group consisting of europium, terbium,praseodymium, samarium, dysprosium, holmium, erbium, thulium, neodymiumand ytterbium.
 15. A method of determining the temperature of a locationwithin a biological body, comprising the steps of:providing a length ofoptical fiber, positioning a layer of phosphor material at one end ofsaid optical fiber to form a temperature probe thereon, the phosphormaterial being characterized by emitting, when excited, detectableoptical radiation that varies as a known function of the phosphortemperature, placing said temperature probe within a biological body,exciting said phosphor to cause emission of said opticalradiation,directing said phosphor emission through said optical fiber toa detecting station at another end of the optical fiber, and detectingat the detecting station the intensity of said optical radiation,whereby said intensity is an indication of the temperature of thephosphor material layer and related thereto by said known temperatureemission function.
 16. A method according to claim 15 comprising anadditional step of irradiating a portion of the biological body in whichthe probe is placed with heat generating radiation.
 17. A temperatureprobe system, comprising:an optical fiber bundle having at least onedistinct group of one or more fibers for optically conducting lightbetween one end thereof and the other; a temperature sensitive elementlocated at said one end of said optical fiber bundle, said temperaturesensitive element having temperature sensitive luminescent propertiesand being adapted to be positioned in the environment whose temperatureis to be measured; means for exciting said temperature sensitive elementto luminescence; and light responsive detection means located at theother fiber bundle end for detecting light directed from saidtemperature sensitive element and passed through said optical fiberbundle.
 18. A temperature probe system, comprising:an optical fiberbundle having a first group and a second group of one or more opticalfibers which are physically separated at one end of said bundle; atemperature sensitive element having temperature sensitive luminescentproperties, said temperature sensitive element being located at theother end of said bundle in optical communication with both first andsecond groups thereof and being adapted to be positioned in theenvironment whose temperature is to be measured; a light source locatedproximate said first group of optical fibers at said one end of saidbundle, said light from said source optically passing through said firstbundle to excite said temperature sensitive element; and lightresponsive detection means located proximate said second group ofoptical fibers at said one end of said bundle, said light emitted fromsaid temperature sensitive element passing through said second bundle tosaid light responsive detection means.
 19. A temperature probe system,comprising:an optical fiber bundle having at least one optical fiber; atemperature sensitive element having temperature sensitive luminescentproperties when excited by a light source and having the property ofemitting light during luminescence at a different frequency than that itabsorbs, said temperature sensitive element being located at one end ofsaid bundle and being adapted to be positioned in the environment whosetemperature is to be measured; an exciting light source locatedproximate the other end of said bundle, said light source having a givenfrequency spectrum that includes a frequency absorbed by saidtemperature sensing element; means proximate said other end forseparating the light passed from said source toward said temperaturesensitive element from that being emitted from said temperaturesensitive element; and light responsive detection means locatedproximate said other end of said bundle, said light responsive detectionmeans including means for detecting a characteristic of the lightemitted from said light sensitive element as a function of the change intemperature of said temperature responsive element.
 20. The temperatureprobe according to claim 19 wherein said separating means includes abeam splitter and an excitation frequency filter associated with saidsource and a luminescent response filter associated with said lightresponsive detection means.
 21. A temperature probe system,comprising:an optical fiber bundle having at least one optical fiber; atemperature sensitive element having temperature sensitive luminescentproperties, said temperature sensitive element being located at one endof said bundle and being adapted to be positioned in the environmentwhose temperature is to be measured; a radioactive source locatedproximate said temperature sensitive element for exciting saidtemperature sensitive element; and light responsive detection meanslocated proximate the other end of said bundle for detecting theemission response of said temperature sensitive element as a function ofits temperature.
 22. The temperature probe according to any of claims17, 18, 19 or 21 wherein said temperature sensitive element includes aphosphorescent material.
 23. The temperature probe according to any ofclaims 17, 18, 19 or 21 wherein said temperature sensitive elementincludes a phosphor material encapsulated in an optically opaqueelement.
 24. The temperature probe according to any of claims 17, 18, 19or 21 wherein said temperature sensitive element includes a phosphormaterial having a luminescent response which is temperature dependent.25. A temperature probe system, comprising:an optical fiber bundlehaving at least one optical fiber; a temperature sensitive elementhaving radioactive and luminescent temperature sensitve properties, saidtemperature sensitive element being located at one end of said bundleand being adapted to be positioned in the environment whose temperatureis to be measured; and light responsive detection means locatedproximate the other end of said bundle for detecting the emissionresponse of said temperature sensitive element as a function of itstemperature.
 26. The temperature probe according to claim 24 whereinsaid temperature sensitive element is a radioactivated phosphormaterial.
 27. The combination of any of claims 17, 18, 19, 21 and 25wherein the luminescence of the temperature sensitive element ischaracterized by relative intensities within two optically isolatablebandwidths that vary as a known function of the element's temperature,and further wherein said detection means includes means for detectingthe luminescent intensity of the temperature sensitive element withineach of said two bandwidths, and means for comparing the levels ofintensity within said bandwidths, wherein said comparison provides anindication of said element's temperature.